PURPOSE: To prevent the positioning accuracy of a base to be positioned from being deteriorated by the fluctuation of the external size of the base and foreign matters adhering to the outer periphery of the base by positioning the base by putting a pair of positioning pins in a pair of openings formed in the base so that the base can be positioned on the line connecting the openings to each other.

CONSTITUTION: A pair of positioning pins 25 and 32 are arranged so that they can be counterposed to each other and can be brought nearer to and separated from each other and, when a base 2 is fed to the space between the pins 25 and 32, the pins 25 and 32 get in a pair of openings formed in the base 2 and, at the same time, position the base 2 by holding the base 2 between them.